This invention is directed to apparatus for reducing surface turbulence in a molten metal bath, and more particularly, to impact pads for controlling the fluid flow pattern of an incoming ladle stream for the purpose of reducing surface turbulence within a continuous caster tundish.
Tundishes, located between the ladle delivering liquid steel to the caster floor and the continuous caster mold, are large containers for holding a reservoir of liquid steel. The liquid steel is transferred from the ladle through a ladle shroud extending into the tundish, and the liquid steel is fed at a continuous or semicontinuous flow rate controlled by a stopper rod, or by a slide gate assembly.
Extensive water flow-model studies have been made throughout the steelmaking industry to simulate liquid steel fluid flow patterns within an actual tundish. These water flow-models have been beneficial in determining critical areas of tundish design such as depth of bath, well block locations, and placement of fluid flow control devices within the tundish. As a result of these studies, it is well-known that the fluid flow generated by the incoming ladle stream is reflected from the flat tundish floor toward the surface of the liquid steel. This generated fluid flow causes a turbulent boiling action and extensive wave motion at the surface of the steel bath. Additionally, where the fluid flow forces are obstructed by structural barriers such as tundish side and end walls, the ladle stream fluid flow surges upward, along such barriers, and causes excessive turbulence at the surface of the liquid steel bath. The excessive turbulence produced by the upward surge breaks up the tundish flux cover, and produces a downward surge around the ladle shroud. The broken flux cover allows the liquid steel to be exposed to the atmosphere which sets up conditions conducive to altering the chemistry of the steel bath. The chemical changes typically involve loss of aluminum from the bath and/or absorption of oxygen and nitrogen into the steel. The downward, shear flow of the liquid steel swirling around the ladle shroud, entraps particles from the broken slag cover within the ladle stream.
Surface requirements, and cleanliness standards for modern high quality steel products, dictate that impurities and chemical changes can not be tolerated within the product. Heretofore, there have been various attempts to reduce or eliminate surface turbulence within a continuous caster tundish to improve the quality of the finished steel product. These attempts have included a wide assortment of dams and weirs which redirect the ladle stream fluid flow away from the surface of the bath. One such attempt, comprising wall dams extending along the tundish sidewalls near the surface of the liquid steel bath, is disclosed in Applicant's prior U.S. Pat. No. 4,715,586 granted Dec. 29, 1987. Although many past fluid flow control devices have been somewhat successful in controlling fluid flow and reducing surface turbulence, they tend to cause operational problems. Caster operators have found that wall dams are difficult and expensive to install and maintain. The operators have also discovered, that because of their location within the tundish, and because of their high profiles, the past flow control devices interfere with tundish deskulling apparatus, and are damaged, or destroyed during the deskulling operations.